1. Field of the Invention
The present invention relates to an information processing apparatus and method and, in particular, to an information processing apparatus and method which may easily keep PCR jitter low in a receiver for digital broadcasting, which processes a multiplexed transport stream, for example, obtained by multiplexing multiple transport streams containing a PCR (Program Clock Reference) packet describing a time, for example.
2. Description of the Related Art
In a transmitter used for digital broadcasting such as a BS (Broadcasting Satellite) and a CS (Communications Satellite), multiple transport streams (TS) are time-division multiplexed, and the resulting multiplexed transport stream is transmitted.
FIG. 1 shows a configuration example of a part of a transmitter 1 for digital broadcasting.
In FIG. 1, the transmitter 1 includes a multiplexer section 11.
As the multiple transport streams, eight transport streams, that is, transport streams #0 to #7 are supplied to the multiplexer section 11.
Here, each of the transport streams contains MPEG data resulting from MPEG (Moving Picture Experts Group) encoding of an image or voice or a PCR packet as time information describing times.
The multiplexer section 11 time-division multiplexes the transport streams #0 to #7 supplied thereto and outputs the resulting multiplexed transport stream.
Then, the transmitter 1 performs predetermined processing on the multiplexed transport stream output from the multiplexer section 11 and outputs the resulting broadcasting signal.
Notably, in the multiplexer section 11, a maximum of eight transport streams for one band are time-division multiplexed. Thus, in order to transmit one program by one transport stream, a maximum of eight programs can be transmitted simultaneously in one band.
Though a case where one program is transmitted by one transport stream will be described below, multiple programs can be transmitted by one transport stream alternatively.
FIG. 2 shows the multiplexed transport stream.
In FIG. 2, the multiplexed transport stream contains multiple frames, and one frame corresponds to a time equal to about 1.38 ms. The frame has multiple slots, that is, 48 slots including slots #1 to #48. The time-division multiplexing of transport streams is performed in slots.
The size of a slot (data length) is fixed to 204 bytes. The first one byte of a slot is 47H in base 16, that is, 0100011 in base 2 and functions as a synchronization signal in MPEG 2.
In transmitter 1, which transport stream is to be assigned to which slot, that is, the assignment of a transport stream to a slot is arbitrary and is performed based on a predetermined assignment.
The multiplexer section 11 of the transmitter 1 assigns the transport streams #0 to #7 to the slots #1 to #48 based on a predefined assignment.
FIG. 3 shows a state where the transport streams #0 to #7 are assigned to the slots #1 to #48.
In FIG. 3, the transport stream #0, transport stream #1 and transport stream #2 are assigned to the slots #2 and #47, slots #1 and #48 and slot #3, respectively, for example.
Notably, the transmitter 1 can change the setting of the assignment of transport streams to slots. However, the assignment is constant in each frame of a super frame (SF) containing eight frames.
TMCC (Transmission and Multiplexing Configuration Control) information of ISDB (Integrated Services Digital Broadcasting), which is control information including information describing the assignment of transport streams to slots, is added to the beginning of each frame of the multiplexed transport stream.
A receiver that receives a broadcasting signal transmitted from the transmitter 1 includes a demultiplexer, a buffer, and a decoder. The demultiplexer extracts a slot storing data of a preselected program transport stream (which will be called selected transport stream) of a program selected by a user for viewing, for example, from the multiplexed transport stream obtained by performing predetermined processing on the broadcasting signal. The buffer stores the data of the slot extracted by the demultiplexer. The decoder decodes the data of the slot read out and output from the buffer, that is, the data of the selected transport stream.
FIG. 4 shows the multiplexed transport stream to be processed by the receiver.
In FIG. 4, the transport streams #0 and #2 as the selected transport streams are stored in the slots #2, #3 and #47 (shaded in FIG. 4), for example, and the demultiplexer in a receiver extracts and outputs the data of the slots #2, #3 and #47, for example.
Since the data pieces of the slots extracted by the demultiplexer exist so-called intermittently in a frame, the data pieces of the slots to be output by the demultiplexer are intermittent.
When the intermittent data pieces of the slots, that is, the selected transport streams are supplied to the decoder as they are, the PCR packets contained in the selected transport streams are supplied to the decoder at different times, which means that the PCR jitter is high. Therefore, it may be difficult for the decoder to perform normally.
Accordingly, in the receiver, the data pieces of the slots extracted from a frame are temporarily stored in the buffer. Then, the remaining amount of the storage space of the buffer is detected, and control is performed for reading the data pieces of the slots from the buffer so as to keep the remaining amount substantially constant. The data pieces of the slots read from the buffer, that is, the selected transport streams are supplied to the decoder.
Thus, in the receiver, the selected transport streams are serially supplied to the decoder, resulting in the PCR jitter to some extent.
Notably, there have been proposed a method for controlling the recording of a data packet in buffer means based on the number of remaining data packets, which are stored in the buffer means and have not been output yet, and an output signal for controlling the output of the data packets from the buffer means (refer to JP-A-11-234634 (Patent Document 1), for example) and a method for controlling the timing for returning the address of a temporary storage memory to be written by memory control means to the beginning and the timing for returning the address of the temporary storage memory to be read by the memory control means to the beginning (refer to JP-A-2000-35938 (Patent Document 2), for example).